鎖状異種高分子(linear heteropolymers)の統計力学的研究

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Author: 樋渡, 保秋ほか

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Publication date: 1999-03-08

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Note (General)：: 金沢大学自然科学研究科The understanding of the conformational transitionas of biopolymers is a fundamental problem of statistical physics. Protein as well as nuc...

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Material Type: 文書・図像類
Title: 鎖状異種高分子(linear heteropolymers)の統計力学的研究
Author/Editor: 樋渡, 保秋
Hiwatari, Yasuaki
Author Heading: 樋渡, 保秋
Hiwatari, Yasuaki
Publication Date: 1999-03-08
Publication Date (W3CDTF): 1999-03-08
Alternative Title: Statistical study of linear heteropolymers
Periodical title: 平成8(1996)年度科学研究費補助金基盤研究(C) 研究成果報告書概要 = 1996 Fiscal Year Final Research Report Summary
No. or year of volume/issue: 1995-1996
Volume: 1995-1996
Pages: 4p.-
Text Language Code: jpn
Subject Heading: ヘテロポリマー
グロビュール転移
分子の折りたたみ
pairing transition
diblock polyampholyte
protein folding
Monte-Carlo simulation
Target Audience: 一般
Note (General): 金沢大学自然科学研究科
The understanding of the conformational transitionas of biopolymers is a fundamental problem of statistical physics. Protein as well as nucleic acid folding are the main puzzling problems of biological importance. In order to tackle such problems, we undertook a systematic study of polyampholytes so as to understand the relation between the sequence of charges and the observed conformations. The term polyampholyte (designed as PA hereafter) is a generic name describing a polymer chain bearing positively and negatively charged monomers in a given sequence. A coil-globule transition was observed in an alternate polyampholyte. It was recognized that alternate sequences were highly specific and that random sequences should not exhibit any coil-globule transition. For globally neutral sequences, which is the relevant situation to proteins, our general aim is to understand what, in a given sequence, is relevant to conformational transitions. Note that nucleic acids are no PA but polyelectrol ytes (any nucleotide bears the same negative charge), so that the electrostatic interactions do not depend on the sequence of bases but merely on the ionic force.Diblocks and alternate sequences are the two extreme cases among random sequences. For an alternate PA, it is just 0 (except of course for the two monomers in the middle of the chain, but their contribution becomes negligible as the chain length grows). Although long diblocks are far from being the rule among biopolymers (and hereafter it will clearly appear why they don't exist in nature at ordinary temperature) they are nonetheless relevant to the physiccs of biopolymers for the following reason : any sequence of charges generally contains small diblocks spread throughout the chain. The longer the chain, the longer the diblocks. These small diblocks should undergo the earliest transitions (i. e. at the highest temperatures). It seems therefore important to understand the nature of the transitions occurring in diblocks as a function of their size. This is the main issue of the present work.
本研究は、生物分子RNAなどの高次(2次元,3次元)分子構造の形態転移などについて考察する目的から、簡単なモデルとして、等価、等量の正に帯電したモノマーと負に帯電したモノマーからなるポリマー鎖(ポリアンフォーライト)のコイル(C)グロビュール(G)転移をモノテカルロシミュレーション(ボンド揺らぎモデル、BFM)を用いて考察したものである。先ず、BFMモデルを用いて正、負のモノマーが交互に並んだ場合(a-PA)について考察し、比熱などの異常性からCG転移が確認された。次いで、欠陥のあるPAおよびdiblock copolymerについてもモンテカルロシミュレーションを行い、a-PAとの相違について興味ある結果を得た。いづれの場合もa-PAとの場合と同様にCG転移が得られるが、特に興味あるのはdiblock copolymerの場合で、この場合にはCG転移が生じるよりも十分高い温度においても比熱などに異常性が得られる。これは鎖の中央付近を頂点にして2つにおりたたまられるモードに関連している(hairpin stateと呼ぶ)。2次元、3次元モデルのCG転移についても特徴的な相違が発見された。diblock copolymerのグロビュール状態は上の2つ折り状態(hairpin state)から発展・成長していくとかんがえられるからである。その際、局所的にフラストレートした状態が得られ、これを解消していく過程で2次元系では渦巻きの形態が得られる。これら2、3次元系固有の分子の高次構造の形成・転移の本性を明らかにするため、分子の平均の慣性半径、最近接距離、各種分析関数、自由エネルギーなどの計算を行った。また分子構造のダイナミックスについての知見を得るため2つの異なる温度について分子動力学(拘束法)シミュレーションを行った。特に高温の場合はhairpin atateが形成されていく過程が明瞭に観察された。
研究課題/領域番号:07640508, 研究期間(年度):1995-1996
出典：研究課題「鎖状異種高分子(linear heteropolymers)の統計力学的研究」課題番号07640508（KAKEN：科学研究費助成事業データベース（国立情報学研究所））（https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-07640508/076405081996kenkyu_seika_hokoku_gaiyo/）を加工して作成
DOI: 10.24517/00057351
Access Restrictions: 限定公開
Related Material: https://kaken.nii.ac.jp/search/?qm=20019491
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640508/
https://kaken.nii.ac.jp/report/KAKENHI-PROJECT-07640508/076405081996kenkyu_seika_hokoku_gaiyo/
Data Provider (Database): 国立情報学研究所 : 学術機関リポジトリデータベース（IRDB）（機関リポジトリ）
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Original Data Provider (Database): 金沢大学 : 金沢大学学術情報リポジトリKURA